1. Field of the Invention
The present invention relates to a plastic lens suitably used for an optical pickup and the like.
2. Related Background Art
Lenses which are made of plastics have conventionally been used, because they are easy to made and have some other useful reasons. In general, as shown in FIG. 8, such a plastic lens 101 has a brim-shaped flange 103 formed around an optically functioning portion 102. The flange 103 is mainly utilized as an attachment for fixing the lens 101. Also, the lens 101 has an annular wall 104 disposed around the optically functioning portion 102 in order to protect the latter.
For assembling the lens 101 to an optical pickup of a CD-ROM drive or the like, the inclination of the lens 101 is detected and adjusted. An example of process for detecting the inclination of the lens 101 will be explained with reference to FIG. 9. First, the lens 101 is temporarily assembled to a holder 106, and a reflecting glass sheet 105 is placed on the annular wall 104. The upper face of the reflecting glass sheet 105 becomes a reflecting surface which is perpendicular to the optical axis X of the lens 101. Above the reflecting glass sheet 105, near the outer periphery of the lens 101, a photosensor which has a light-sending portion S and light-detecting portion R is disposed. While the lens 101 is rotated together with the holder 106, light is emitted and incidenton the upper face of the reflecting glass sheet 105 from the light-sending portion S. And the light is reflected by the upper face of the reflecting glass sheet 105.
When the lens 101 is not tilted, the emitted light is totally reflected toward the light detecting portion R. In this case, since the light received by the light detecting portion R has a stable predetermined strength, it can be judged that the lens 101 is not tilted.
When the lens 101 is tilted, by contrast, the emitted light is hardly reflected toward the light detecting portion R. In this case, since the light received by the light detecting portion R becomes unstable and weak, it can be judged that the lens 101 is tilted. After the inclination of the lens 101 is adjusted to normal, the lens 101 is bonded and fixed to the holder 106 by an adhesive 107. In the case of a lens without the annular wall 104, a reflecting glass sheet may be formed to be mountable on the lens 101.
Since the conventional plastic lens 101 is assembled to an optical pickup or the like according to the above-mentioned process, it necessitates the step of mounting the reflecting glass sheet 105 on the lens 101 and the step of removing it therefrom. These steps inhibit the inclination of the lens 101 from being adjusted efficiently. Also, since the inclination of the lens 101 is detected and adjusted by way of the reflecting glass sheet 105, errors are prone to occur. Further, when the reflecting glass sheet 105 is deformed or its reflecting surface is damaged, normal detection cannot be effected, thus increasing the time and labor for handling the reflecting glass sheet 105.